First direct determination of the Boltzmann constant by an optical method

International audienceWe have recorded the Doppler profile of a well-isolated rovibrational line in the ν2 band of 14NH3. Ammonia gas was placed in an absorption cell thermalized by a water-ice bath. By extrapolating to zero pressure, we have deduced the Doppler width which gives a first measurement of the Boltzmann constant, kB, by laser spectroscopy. A relative uncertainty of 2x10-4 has been obtained. The present determination should be significantly improved in the near future and contribute to a new definition of the kelvin

Strong Purcell effect observed in single thick shell CdSe/CdS nanocrystals coupled to localized surface plasmons

High quality factor dielectric cavities designed to a nanoscale accuracy are mostly used to increase the spontaneous emission rate of a single emitter. Here we show that the coupling, at room temperature, between thick shell CdSe/CdS nanocrystals and random metallic films offers a very promising alternative approach. Optical modes confined at the nanoscale induce strong Purcell factors reaching values as high as 60. Moreover the quantum emission properties can be tailored: strong antibunching or radiative biexcitonic cascades can be obtained with high photon collection efficiency and extremely reduced blinking.Comment: 16 pages, 7 figure

Photon correlations in the collective emission of hybrid gold-(CdSe/CdS/CdZnS) nanocrystal supraparticles

We investigate the photon statistics of the light emitted by single self-assembled hybrid gold-CdSe/CdS/CdZnS colloidal nanocrystal supraparticles through the detailed analysis of the intensity autocorrelation function $g^{(2)}(\tau)$. We first reveal that, despite the large number of nanocrystals involved in the supraparticle emission, antibunching can be observed. We then present a model based on non-coherent F\"orster energy transfer and Auger recombination that well captures photon antibunching. Finally, we demonstrate that some supraparticles exhibit a bunching effect at short time scales corresponding to coherent collective emission

Intramural Duodenal Haematoma after Endoscopic Biopsy: Case Report and Review of the Literature

The development of intramural duodenal haematoma (IDH) after small bowel biopsy is an unusual lesion and has only been reported in 18 children. Coagulopathy, thrombocytopenia and some special features of duodenal anatomy, e.g. relatively fixed position in the retroperitoneum and numerous submucosal blood vessels, have been suggested as a cause for IDH. The typical clinical presentation of IDH is severe abdominal pain and vomiting due to duodenal obstruction. In addition, it is often associated with pancreatitis and cholestasis. Diagnosis is confirmed using imaging techniques such as ultrasound, magnetic resonance imaging or computed tomography and upper intestinal series. Once diagnosis is confirmed and intestinal perforation excluded, conservative treatment with nasogastric tube and parenteral nutrition is sufficient. We present a case of massive IDH following endoscopic grasp forceps biopsy in a 5-year-old girl without bleeding disorder or other risk for IDH, which caused duodenal obstruction and mild pancreatitis and resolved within 2 weeks of conservative management. Since duodenal biopsies have become the common way to evaluate children or adults for suspected enteropathy, the occurrence of this complication is likely to increase. In conclusion, the review of the literature points out the risk for IDH especially in children with a history of bone marrow transplantation or leukaemia

A novel estrogen-regulated avian apolipoprotein.

In search for yet uncharacterized proteins involved in lipid metabolism of the chicken, we have isolated a hitherto unknown protein from the serum lipoprotein fraction with a buoyant density of ≤1.063 g/ml. Data obtained by protein microsequencing and molecular cloning of cDNA defined a 537 bp cDNA encoding a precursor molecule of 178 residues. As determined by SDS-PAGE, the major circulating form of the protein, which we designate apolipoprotein-VLDL-IV (Apo-IV), has an apparent Mr of approximately 17 kDa. Northern Blot analysis of different tissues of laying hens revealed Apo-IV expression mainly in the liver and small intestine, compatible with an involvement of the protein in lipoprotein metabolism. To further investigate the biology of Apo-IV, we raised an antibody against a GST-Apo-IV fusion protein, which allowed the detection of the 17-kDa protein in rooster plasma, whereas in laying hens it was detectable only in the isolated ≤1.063 g/ml density lipoprotein fraction. Interestingly, estrogen treatment of roosters caused a reduction of Apo-IV in the liver and in the circulation to levels similar to those in mature hens. Furthermore, the antibody crossreacted with a 17-kDa protein in quail plasma, indicating conservation of Apo-IV in avian species. In search for mammalian counterparts of Apo-IV, alignment of the sequence of the novel chicken protein with those of different mammalian apolipoproteins revealed stretches with limited similarity to regions of ApoC-IV and possibly with ApoE from various mammalian species. These data suggest that Apo-IV is a newly identified avian apolipoprotein

Statistical Aging and Non Ergodicity in the Fluorescence of Single Nanocrystals

The relation between single particle and ensemble measurements is adressed for semiconductor CdSe nanocrystals. We record their fluorescence at the single molecule level and analyse their emission intermittency, which is governed by unusual random processes known as Levy statistics. We report the observation of statistical aging and ergodicity breaking, both related to the occurrence of Levy statistics. Our results show that the behaviour of ensemble quantities, such as the total fluorescence of an ensemble of nanocrystals, can differ from the time averaged individual quantities, and must be interpreted with care.Comment: 4 pages, 3 figure

Surpassing the standard quantum limit for optical imaging using nonclassical multimode light

Using continuous wave superposition of spatial modes, we demonstrate experimentally displacement measurement of a light beam below the standard quantum limit. Multimode squeezed light is obtained by mixing a vacuum squeezed beam and a coherent beam that are spatially orthogonal. Although the resultant beam is not squeezed, it is shown to have strong internal spatial correlations. We show that the position of such a light beam can be measured using a split detector with an increased precision compared to a classical beam. This method can be used to improve the sensitivity of small displacement measurements

Receptor-Mediated Gonadotropin Action in Ovary

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65826/1/j.1432-1033.1979.tb12873.x.pd

Surface Doping Quantum Dots with Chemically Active Native Ligands: Controlling Valence without Ligand Exchange

One remaining challenge in the field of colloidal semiconductor nanocrystal quantum dots is learning to control the degree of functionalization or valence per nanocrystal. Current quantum dot surface modification strategies rely heavily on ligand exchange, which consists of replacing the nanocrystal\u27s native ligands with carboxylate- or amine-terminated thiols, usually added in excess. Removing the nanocrystal\u27s native ligands can cause etching and introduce surface defects, thus affecting the nanocrystal\u27s optical properties. More importantly, ligand exchange methods fail to control the extent of surface modification or number of functional groups introduced per nanocrystal. Here, we report a fundamentally new surface ligand modification or doping approach aimed at controlling the degree of functionalization or valence per nanocrystal while retaining the nanocrystal\u27s original colloidal and photostability. We show that surface-doped quantum dots capped with chemically active native ligands can be prepared directly from a mixture of ligands with similar chain lengths. Specifically, vinyl and azide-terminated carboxylic acid ligands survive the high temperatures needed for nanocrystal synthesis. The ratio between chemically active and inactive-terminated ligands is maintained on the nanocrystal surface, allowing to control the extent of surface modification by straightforward organic reactions. Using a combination of optical and structural characterization tools, including IR and 2D NMR, we show that carboxylates bind in a bidentate chelate fashion, forming a single monolayer of ligands that are perpendicular to the nanocrystal surface. Moreover, we show that mixtures of ligands with similar chain lengths homogeneously distribute themselves on the nanocrystal surface. We expect this new surface doping approach will be widely applicable to other nanocrystal compositions and morphologies, as well as to many specific applications in biology and materials science

Molecular Chemistry to the Fore: New Insights into the Fascinating World of Photoactive Colloidal Semiconductor Nanocrystals

Colloidal semiconductor nanocrystals possess unique properties that are unmatched by other chromophores such as organic dyes or transition-metal complexes. These versatile building blocks have generated much scientific interest and found applications in bioimaging, tracking, lighting, lasing, photovoltaics, photocatalysis, thermoelectrics, and spintronics. Despite these advances, important challenges remain, notably how to produce semiconductor nanostructures with predetermined architecture, how to produce metastable semiconductor nanostructures that are hard to isolate by conventional syntheses, and how to control the degree of surface loading or valence per nanocrystal. Molecular chemists are very familiar with these issues and can use their expertise to help solve these challenges. In this Perspective, we present our group\u27s recent work on bottom-up molecular control of nanoscale composition and morphology, low-temperature photochemical routes to semiconductor heterostructures and metastable phases, solar-to-chemical energy conversion with semiconductor-based photocatalysts, and controlled surface modification of colloidal semiconductors that bypasses ligand exchange